1. Field of the Invention
This invention relates to a motor drive system for cameras of the type which include a shutter requiring reciprocative movement of a shutter charge member.
2. Description of the Prior Art
There are known in the art two types of devices for effecting shutter charge in cameras. In the first type of device the shutter charge member is operable in response to a film advance lever to move in one direction until it stops at a certain position. In the second type of device the shutter charge member is operable in response to a film advance lever to move in one direction for shutter charge and then move back in the opposite direction to return to its initial position.
The second type of the device has the advantage of simple construction because the shutter mechanism portion and the film advance system are readily separable from each other. Consequently the shutter mechanism portion can be produced and supplied as a unit separate from the other mechanisms. On the other hand, this type of device suffers from a significant disadvantage. Should shutter release occur before the shutter charge member has completely returned to its initial position, the movement of the shutter mechanism would be interrupted by the charge member thereby causing a great error in exposure time, and possibly resulting in failure of the device. To avoid this, cameras provided with such a reciprocating shutter charge member have been designed such that the charge lever reciprocates in response to movement of the film advance lever, and such that shutter release cannot occur until the film advance lever has completely returned to its initial position. However, development of a simple, reliable motor drive system suitable to be utilized in such cameras has been difficult because of the complexity of the operation cycles. A motor drive system for use with a camera having the first type of shutter charging device involves only two cycles of operation, i.e. rotating a film advance and shutter charge shaft in one direction to effect film advance and shutter charge and thereafter releasing the shutter, whereas in the case of a device of the second type there are involved three cycles of operation, that is, rotating the film advance and shutter charge shaft in one direction to effect film advance and shutter charge, then rotating the shaft in the opposite direction to return the advance lever and shutter charge member to their initial positions (this intermediate cycle being hereinafter referred to as "resetting" or the "lever return cycle"), and thereafter releasing the shutter.